The purpose of this project is to study the physical properties of a wide variety of biological macromolecules with the goal of correlating these properties to the structure and function of the macromolecules. The emphasis is on the thermodynamics of the interactions of these macromolecules and on their molecular size and shape. Analytical ultracentrifugation and mathematical modeling are the principal research techniques used. The studies on the binding of plasminogen by fibrinogen described in the 1983 report have been published. Studies currently in progress in this area deal with the association of plasminogen with plasmin inhibitor, with the association of plasminogen with the D and E fragments of fibrinogen and with the association of fibrinogen with plasma Factor XIII. Studies on the association of the A and B chains of reduced ricin indicate that the formation of the AB complex is reversible and that the complex undergoes further reversible self-association to form polymers up to octomer. The temperature dependence of these reactions indicates that they are entropically driven, suggesting strong hydrophobic interaction between the chains. Studies on the retinoid-binding protein from the interphotoreceptor matrix of the retina of macaque monkeys demonstrate that this is a significantly asymmetrical, hydrophobic glycoprotein with a molecular weight of 106,000.